Electronic control of transmission systems for industrial vehicles is a well established method of controlling acceleration and deceleration. In conventional applications, a transmission controller is often used to automatically engage or shift transmission clutch packs when the vehicle travel speed reaches a certain threshold, for example. Similarly, the transmission controller may initiate a form of clutch pack braking to assist in decelerating the vehicle. For industrial vehicles such as lift trucks, in particular, great demands are placed on the transmission system by the operator under normal materials transport applications. For example, the lift truck operator is required to change directions frequently, vary speeds from fine incremental adjustments at low speeds to relatively high speeds, lift and transport heavy loads, and all the while controlling a myriad of hydraulic functions which are dependent on engine speed for supplying hydraulic pressure and flow.
Control of the transmission and engine speed has conventionally been managed in part by a transmission controller, an engine controller, and the operator in order to provide the operator with maximum flexibility and control of the lift truck operation. As such, conventional lift trucks include an accelerator pedal, an inching/brake pedal, and a separate brake pedal, which allow for the simultaneous control of both engine speed and vehicle travel speed, thereby providing for independent control of the hydraulic functions and vehicle travel speed. This is especially important when traveling at low vehicle travel speeds, or when operating the lift truck on an incline, for example. At low vehicle travel speeds, the engine speed is typically operating at a reduced rpm, and significant hydraulic function demands can result in engine drag that will ultimately cause the engine to stall if the engine speed is not increased accordingly. Similarly, operation of a lift truck on an incline poses the additional difficulty that the lift truck will tend to accelerate down the incline due to gravity which contradicts the operator demand for incremental fine adjustment at a low speed in order to position or handle a load.
Conventional transmission systems require considerable skill and training by the operator to use multiple foot pedals while at the same time operating three or more hand levers or controls, in order to simultaneously control engine speed, vehicle acceleration and braking, and hydraulic function. In addition, as brake shoes and other components wear during normal operation, regularly schedule maintenance of the braking, inching, and hydraulic function interaction are administered to ensure proper lift truck operation. The demands placed on the transmission from these types of applications often result in high energy absorption requirements in the transmission and engine, and when the energy absorbed exceeds the ability of the cooling system, the transmission and engine systems will run hot and lead to more frequent servicing and premature component failure.
Under these materials handling conditions, therefore, conventional lift trucks require significant and additional operator skill and training, at best, and provide potential to damage a load or overheat the lift truck, at worst. The present invention addresses these and other problems associated with the prior art.